Digital communications have become increasingly common as digital control devices are used in controlling a wide range of consumer products from automobiles to washing machines. Typically, a microprocessor-based controller will communicate with an externally controlled device to carry out a function or to receive some information. The controller and controlled device send and receive data to the other via a single communication link cable.
However, communication problems may occur when the send and receive messages conflict with each other. This type of problem is commonly due to two characteristics of this type of communication. One characteristic pertains to the start time for a message. For example, neither communicator knows when the other is going to begin transmitting a new message. Thus, if both communicators attempt to send data to each other simultaneously, then a collision may occur which can destroy the integrity of the data. It is then desirable to detect when a communicator is receiving a message in order to delay the transmission of a subsequent message to avoid any collision.
A second characteristic pertains to the message delay associated with the baud rate of the data transmission and the length and/or load capacitance of the cable. For example, each communicator includes transmit and receive circuitry. When a message is transmitted from one communicator to another communicator, the receive circuitry of the transmitting communicator also detects its own transmissions after some measurable delay has passed. This delay is dependent upon the baud rate of the message and the load capacitance and/or the length of the cable. It is therefore important to avoid detecting a communicator's own delayed transmission because otherwise a false collision detection at that communicator would occur. Thus, it is desirable to account for the delay from the production of the transmission signal to the receipt of the delayed transmission signal in order to avoid false detections associated with that delay.
The present invention is directed toward overcoming one or more of the problems as set forth above.